The present invention is directed to stable anionic aqueous emulsions of organopolysiloxane particles having a volume average particle diameter (Dv) of at least about 300 nanometers (nm) and consisting essentially of chemically combined aminoorganosiloxy functional units and diorganosiloxy units. More particularly, the present invention is directed to a method involving the reaction of an aqueous acid catalyzed emulsion of organopolysiloxane particles with an amine functional organosilicon material.
There is shown in U.S. Pat. Nos. 5,726,270, 5,856,402, and 5,900,460 to Craig, semi-continuous methods for making acid catalyzed aqueous dispersions of organopolysiloxanes useful in coating applications, including personal care. For example, in the formulation of a silicone-containing hair shampoo, experience has shown that desirable results can be achieved with aqueous dispersions of organopolysiloxane particles having a volume average particle diameter in the range of at least about 300 nanometers to about 1 micron. It has been found that improvements in hair styling with silicone-containing shampoos can be achieved in particular situations as a result of the "smoothing out" effect. It is speculated that silicones in the form of aqueous dispersions of organopolysiloxane particles having an average diameter of at least about 300 nanometers can more readily coat the surface of the hair shaft.
Experience also has shown that further benefits in coating and in personal care applications can be obtained with aqueous dispersions of organopolysiloxane particles if the dispersed particles are modified with a functional group, such as aminoorgano, epoxy, carboxy, or mercapto. However, previous efforts to functionalize such organopolysiloxane particles during their initial formation from cyclic poly(diorganosiloxane) under semi-continuous conditions, often resulted in functionalized organopolysiloxane particles with a volume average particle diameter less than about 300 nanometers. In particular, although an aqueous emulsion of organopolysiloxane particles having a volume average particle diameter of at least about 300 nanometers can be generated under semi-continuous conditions by the acid catalyzed equilibration of cyclic poly(diorganosiloxane) in the absence of the amine functionalized organosilicon source material, efforts to functionalize the particles during the initial particle formation under semi-continuous conditions in the presence of an amine functionalized organosilicon source material typically results in particles having a volume average particle diameter less than about 300 nanometers.
Further, a procedure for making an acid catalyzed aqueous dispersion of organopolysiloxane particles with aminoorgano functional groups involves working with competing anionic and cationic charges. In addition to adversely affecting particle size, amine functionalization efforts also can impact adversely on emulsion stability and acid-catalyzed polymerization rates. In particular, emulsion instability is favored as a result of the presence of aminoorgano functional groups, and anionic silicone emulsion particles as shown by U.S. Pat. No. 5,045,576. A satisfactory method is therefor needed to make stable aqueous emulsions of amine functionalized organopolysiloxane particles having a volume average particle diameter of at least about 300 nanometers using an acid catalyzed process.